Nearly 3,000 people were killed when alleged al-Qaeda operatives hijacked four passenger planes and crashed them into New York's World Trade Center, the Pentagon and a Pennsylvania field.

The suspects face charges that include mass murder.

Khalid Sheikh Mohammed

Born in Kuwait to Pakistani parents, Mohammed was educated in the US. Prosecutors contend he was a military operations commander for al-Qaeda's foreign operations before his capture in Pakistan in 2003.

Known as KSM, he is alleged to have claimed responsibility for 31 attacks or planned attacks and told the US military that he was responsible for the September 11 attacks "from A to Z". He has also claimed responsibility for the killing of Wall Street Journal reporter Daniel Pearl.

According to the charges against him, Mohammed is alleged to have "masterminded the attacks by proposing the operational concept to Osama bin Laden as early as 1996, obtaining approval and funding from Osama bin Laden for the attacks, overseeing the entire operation, and training the hijackers in all aspects of the operation in Afghanistan and Pakistan".

Walid bin Attash

A Yemeni raised in Saudi Arabia, Attash lost his right leg in a 1997 battle in Afghanistan. He stands accused of running an al-Qaeda camp in Afghanistan where he trained two of the September 11 hijackers. He is alleged to have travelled to Malaysia in 1999 to observe US airline security in order to assist the hijacking plan.

He is also accused of financing the 2000 attack in Yemen on the USS Cole, buying the boat and explosives used in the attack and recruiting the operatives, of helping to obtain a passport for a man involved in the 1998 bombing of the US embassy in Kenya, and acting as the link between bin Laden and the leader of al-Qaeda's Kenya cell.

Ramzi Binalshibh

A Yemeni national, Binalshibh is alleged to have lived in Hamburg, Germany, with several of the hijackers responsible for the 2001 attacks in the US, and to have served as a link between al-Qaeda leaders and the hijackers.

US officials allege he was originally selected by Osama Bin Laden to be one of the hijackers, and made a "martyr video" in preparation for the attack. After being refused entry to the US, he is alleged to have helped find flight schools for the hijackers in the US and "engaged in numorous financial transactions" to support the hijackers.

Binalshibh was captured in Karachi, Pakistan, in September 2002. Military doctors diagnosed him with a delusional disorder, and defence lawyers have challenged his mental competency for trial.

Ali Abdul Aziz Ali

Also known as Ammar al-Baluchi, the Pakistani national is a nephew of Khalid Sheikh Mohammed and cousin of jailed 1993 World Trade Center bomber Ramzi Yousef.

He is accused of being an important facilitator of the September 11 attacks, transferring money to US-based operatives and assisting nine hijackers on their way from Pakistan to the United States. The Pentagon said he sent about $120,000 to hijackers for their expenses and flight training.

Mustafa Ahmed al Hawsawi

The Saudi citizen is accused of being a key financial facilitator of the September 11 attacks. US officials say allege that he provided the hijackers with money, Western clothing, travellers' cheques and credit cards. He is alleged to have accepted about $20,000 in wire transfers from two of the September 11 hijackers in the days before the attack.

The US military said his laptop held files that included al-Qaeda expense reports and details of al-Qaeda operatives and their families. He has said he was not a member of al-Qaeda but attended an al-Qaeda training camp in Afghanistan and supported all "jihadists".